1. Field of the Invention
This invention relates to a pressure resistant square panel made of steel or cast iron and more particularly to a pressure resistant square steel or iron panel for use in panel assembled water tanks.
2. Description of the Prior Art
Panel assembled water tanks have been widely used, located at high levels as for example on roofs of high buildings for water reservoirs or underground for waste water. Plastic coated steel panels or glass fiber reinforced plastic panels have been preferably used for the panel assembled water tanks. Steel panels inter alia are suitable for large water tanks because of their conspicuous strength. Such steel panels are usually formed in their pressure receiving square surfaces with reinforcing ribs for the purpose of further increasing the pressure resistance of the panels by reducing deformations to much smaller values which would be caused by the water whose pressure tends to bulge the panels of the assembled tanks. The reinforcing ribs are generally often formed along their diagonals in substantially X-shaped ribs as viewed in planes in order to facilitate manufacturing the panels. However, the steel panels reinforced by ribs hitherto used are not necessarily satisfactory in strength characteristics required for assembled tanks. On the other hand, panel assembled tanks have become progressively larger according to requirements. Under such conditions it has been expected to develop higher pressure resistant panels suitable for panel assembled tanks.